1. Field of the Invention
The present invention relates to a video signal recording and reproducing apparatus, and in particular to a component video signal magnetic recording and reproducing apparatus of the baseband recording type with a plurality of channels.
2. Description of the Prior Art
Video signal recording and reproducing apparatuses that have been developed and find applications include a VTR (video tape recorder) with magnetic tape used as a recording medium and a video disc with a magnetic disk (or optical disk) used as a recording medium. Especially, the VTR technology has recently become so advanced that the ownership of VTR's for home-use has greatly expanded.
VTR's are roughly classified into direct recording system and color-under recording system. The former system directly uses the video signal (a composite signal with luminance signal and carrier chrominance signal multiplexed with each other) for FM modulation. In the latter method, on the other hand, the carrier chrominance signal and the luminance signal in the video signal are separated from each other, and the luminance signal alone is FM-modulated, while the carrier chrominance signal is frequency-converted to low frequency and multiplexed with the FM luminance signal for recording. Generally, the direct recording system is used for high-class VTR which can obtain a high-quality reproduced picture. Although it produces a high-quality picture, the device is bulky and tape consumption is great, thereby leading to a high cost. The color-under recording system, on the other hand, with compact hardware, is smaller in tape consumption and cost and therefore finds application mainly as a home-use VTR. Though natural, the picture quality of this color-under recording system is lower than the direct recording system.
In view of this situation, research is being conducted on various systems which are compact in hardware, low in cost and tape consumption and can produce a high-quality reproduced picture at the same time. One of them is a method in which the color difference signals are processed in the baseband state and split for recording by a couple of heads. The baseband processing eliminates the need for a time base corrector required for the direct recording system to correct the phase change of the chrominance subcarrier and prevents deterioration of the color information which otherwise might occur in the color-under recording system.
If the recording system is to be configured of small hardware, the diameter of the head cylinder must be reduced. In the case of a small head cylinder, however, the frequency band width for recording and reproducing is limited, so that it becomes difficult to record and reproduce the luminance signal and the two color difference signals in a single track. For this reason, they are recorded and reproduced in two tracks.
The system will be explained with reference to FIG. 1 as a conventional example capable of recording and reproducing a high-quality picture with small hardware and comparatively small tape consumption. FIG. 1 is a block diagram of a VTR of the baseband-processed two-channel recording type mentioned above. In FIG. 1, reference numeral 1 designates an input terminal, numeral 2 a decoder, numeral 3 a luminance signal, numeral 7 an (R-Y) signal, numeral 8 a (B-Y) signal, numeral 4 a luminance signal recording processor (designated as "Y-PROC" in FIG. 1), numeral 5 an FM modulator, numeral 9 a multiplexer, numeral 10 a color difference signal recording processor (designated as "C-PROC" in FIG. 1), numeral 11 an FM modulator, numerals 6 and 12 recording heads, numeral 13 a magnetic tape, numerals 14 and 18 playback heads, numeral 15 an FM demodulator, numeral 16 a luminance playback processor (designated as "Y-PROC" in FIG. 1), numeral 17 a luminance signal, numeral 19 an FM demodulator, numeral 20 a color difference signal reproducing processor (designated as "C-PROC" in FIG. 1), numeral 21 a demultiplexer, numeral 22 an (R-Y) signal, numeral 23 a (B-Y) signal, numeral 24 an encoder and numeral 25 an output terminal.
The video signal to be recorded is applied through the input terminal 1 to the decoder 2. The decoder 2 decodes the applied video signal into the luminance signal 3, (R-Y) signal 7 and (B-Y) signal 8. The two color difference color-difference signals handled are assumed to be the (R-Y) signal and the (B-Y) signal.) The luminance signal picked up at the decoder 2 is applied to the luminance signal recording processor 4. The luminance signal recording processor 4, having pre-emphasis, clip and clamp processes, applies an output to the FM modulator 5 for FM modulation, after which the signal is recorded in the magnetic tape 13 through the recording head 6. The two color difference signals including (R-Y) signal 7 and (B-Y) signal 8 picked up at the decoder 2, on the other hand, are both applied to the multiplexer 9. The (R-Y) signal 7 and the (B-Y) signal 8 applied to the multiplexer 9 are multiplexed by time division multiplex (for example, the (R-Y) signal 7 and the (B-Y) signal 8 are compressed to half along the time axis and multiplexed in series.), and after that, supplied to the color difference recording processor 10. The color-difference recording processor 10, having such processes as pre-emphasis, clip and clamp, applies the signal to the FM modulator 11, after which the signal is recorded on the magnetic tape 13 through the recording head 12.
In playback mode, the information corresponding to the luminance signal recorded on the magnetic tape 13 is picked up through the playback head 14 and demodulated by the FM demodulator 15. The demodulated signal is de-emphasized or clamped at the luminance playback processor 16, and then applied as the luminance signal 17 to the encoder 24. On the other hand, the information corresponding to the color difference signal recorded on the magnetic tape 13 is picked up through the playback head 18 and demodulated by the FM demodulator 19. The demodulated signal, after being de-emphasized or clamped at the color difference playback processor 20, is applied to the demultiplexer 21. The demultiplexer 21 converts the multiplexed signals back to an (R-Y) signal and a (B-Y) signal in the normal time axis, and after that, the resulting (R-Y) signal 22 and the (B-Y) signal 23 are applied to the encoder 24. The encoder 24 produces a composite video signal on the basis of the luminance signal 17, (R-Y) signal 22 and the (B-Y) signal 23 and supplies a reproduced video signal through the output terminal 25.
The conditions of respective parts are shown in FIG. 2. In FIG. 2 showing waveforms produced at the parts included in FIG. 1, numeral 26 designates a luminance signal waveform, numeral 27 an (R-Y) signal waveform, numeral 28 a (B-Y) signal waveform, numeral 29 a multiplexed color difference signal waveform, numeral 30 a horizontal scan period, numeral 31 a horizontal synchronization signal, numeral 33 a time-axis-compressed (R-Y) signal, numeral 34 a time-axis compressed (B-Y) signal and numeral 32 a color difference synchronization signal. In FIG. 1, the luminance signal 3, (R-Y) signal 7 and (B-Y) signal 8 correspond to the waveform 26, waveform 27 and waveform 28 respectively, while the output of the multiplexer 9 corresponds to the waveform 29. In the absence of deterioration in recording and playback, the luminance signal 17, (R-Y) signal 22 and the (B-Y) signal 23 of course correspond to the waveforms 26, 27 and 28 respectively, and the signal applied to the demultiplexer 21 to the waveform 29.
The information frequency band of the prior art mentioned above will be discussed below.
Generally, if a high-quality reproduced picture is to be obtained, the luminance signal 3 requires a frequency band of about 4 MHz, the (R-Y) signal 7 and the (B-Y) signal 8 about 1.3 MHz respectively. Then, the bandwidth of the signal applied to the FM modulator 5 is about 4 MHz. On the other hand, since the color difference signals are multiplexed by being compressed half in time, the signal bandwidth applied to the FM modulator 11 is about 2.6 MHz (1.3 MHz.times.2). If the magnetic heads and magnetic tape are considered to be a transmission path, the transmission bandwidth of this transmission path is determined substantially by the minimum wavelength and relative speeds of the magnetic heads and magnetic tape capable of recording and reproduction. In the conventional system shown in FIG. 1, the luminance signal and the color difference signals of course are recorded at the same relative speeds, and therefore they have substantially the same frequency bandwidth to be recorded and reproduced. Nevertheless, as mentioned above, the frequency bandwidth of the luminance signal 3 is about 4 MHz, while it is only about 2.6 MHz at the output of the multiplexer 9. In other words, the design of the luminance signal transmission system is very marginal, while the color-difference signal transmission system has an ample margin in its design. That is to say, the great problem of the prior art system shown in FIG. 1 is that for lack of balance of frequency bandwidth between the luminance signal system and the color difference signal system, the color difference signal system has an ample margin while the luminance signal system has a very marginal recording and playback operation. As a consequence, the magnetic tape is not utilized efficiently as a recording medium.